In 3GPP (3rd Generation Partnership Project), the packet-switched communication systems HSPA (High Speed Packet Access) and LTE (Long Term Evolution) have been specified for wireless transmission of data packets between user terminals and base stations in a cellular/mobile network. In this description, the term “base station” is used to generally represent any system entity capable of wireless communication with a user terminal. A base station of a cell in a wireless network may transmit data and control information in a physical downlink channel to a user terminal or “UE” (User Equipment), and a user terminal may likewise transmit data and control information in a physical uplink channel in the opposite direction to the base station. In this description, a physical downlink or uplink channel is generally referred to as a wireless link between a sending entity and a receiving entity. Further, the terms “sending entity” and “receiving entity” are used here merely to imply the direction of the wireless link considered, although these entities can of course both receive and send data and messages in an ongoing communication.
LTE systems generally use DFT-SFDMA (Discrete Fourier Transform-Spread Frequency Division Multiple Access) in uplink. The DFT-SFDMA transmission technique, is considered an effective technique in high-bit-rate data due to its spectral efficiently, it robustness in different multipath propagation environment, and its low PAPR (Peak-to-Average-Power-Ratio). However, a well-known problem of DFT-SFDMA is its vulnerability to the frequency offset (FO) including carrier frequency offset (CFO) resulting from the mismatch between the carrier frequencies at the transmitter and receiver. There are numerous estimation methods for CFO correction. Some of them are focused on the estimation accuracy, but the estimation range is then limited. Other methods are instead focused on a wider estimation range, but then the accuracy is not reliable enough. It is very difficult to balance the accuracy and range in the real system. In the invention, according to the frame structure of the LTE uplink, both estimation range and accuracy for CFO correction are considered.
With “resource block” is meant the smallest time unit possible to schedule for a user. Typically, a user occupies one or more resource blocks, as seen in FIG. 1. Each resource block consists of a grid with 14 resource symbols on one axis and 12 resource elements on the other axis.
It is thus generally a problem that in communication in uplink according to DFT-SFDMA based structures, the carrier frequencies for the resource elements are affected by various frequency offsets between the receiving system entities and the sending system entity, which disturbs the communication.